The present invention relates to a protective material for electronic parts and devices, and a process for the production of electronic devices utilizing the protective material. More specifically, the invention relates to a protective material which can exhibit a remarkable characteristic of protecting electronic parts, for example semiconductor elements formed on semiconductor substrates, in mechanically grinding or chemically etching the semiconductor substrates and yet can be stripped or removed with ease. The material is also useful for a protective film for protecting for example liquid-crystal display plates against deposition of dust or the like. The invention also relates to a process for the production of electronic devices while a necessary protection of the devices is effected with use of the protective material.
It is conventionally practiced in preparation for the production of chips by cutting a semiconductor plate such as for example a silicon wafer having semiconductor elements, electrodes and so forth formed thereon to mechanically grind or chemically etch a backside surface of the semiconductor plate to process this plate to the prescribed thickness and smoothen its backside surface.
Regardless whether it is done by a mechanical grinding method or by an etching method using a chemical, such processing of semiconductor substrates is carried out in the condition in which a device side surface of the plates on which semiconductor elements and so forth are arranged is protected by a covering of a protective film so that the device side surface can be protected against impairing or any other adverse affect.
The protective film for use as above is required to possess the following characteristics.
(1) It is tough enough not to become broken through a mechanical grinding.
(2) It is resistant against acids used as etchant in chemical etching.
(3) After it is used in a grinding or etching step, it can be easily stripped or removed with chemicals which are not corrosive of semiconductor elements, interconnection elements and so forth.
In the prior art, it is known to use for the protective material a cyclized rubber based negative photoresist or a novolak resin based positive photoresist, for example from Japanese patent application Kokai publication Nos. 54-41068, 57-10933, 57-192031, 59-117219 and 61-110435.
However, the known protective materials are not fully satisfactory: With cyclized rubber based nagative photoresists, while they have remarkable toughness and acid resistance as a protective film, they inconveniently involve the need of using harmful phenol or chlorinated olefins in removing them after they are used in the process for etching. In addition, they are hardly removable and a relatively long time has to be consumed in removing them. With novolak resin based positive photoresists, then, not only their strength or toughness as a protective film is so poor that they are prone to become broken relatively with ease but also their acid resistance is relatively limited. Also, alike the above cyclized rubber based negative photoresits, the novolak resin based positive photoresists, too, involve the need of using a chemical exclusively for their removal.
Further, it is also widely practiced to apply protective films over surfaces of various electronic parts and devices such as semiconductor substrates, liquid crystal display plates and so forth so that they can be prevented from undergoing deposition of dusts or the like present in the atmosphere, as needs be possibly when they have to be kept in stock or they are packaged and shipped. For protective films for such use, too, the above-mentioned known protective materials are utilized, which however are found to fail to be satisfactory with respect to both of the mechanical strength and the removability after service.